Method of lumber preparation to improve drying and development of a new engineered wood composite

ABSTRACT

A method of treating a piece of lumber including the steps of a) analyzing the lumber to detect a surface defect at a site on the lumber; b) removing at least a portion of the surface defect to form an opening in the lumber at the site of the defect; c) drying the lumber using a process wherein moisture is allowed to escape from the lumber through the opening; and, d) inserting a solid plug in the opening to refill the opening in the lumber.

FIELD OF THE INVENTION

The invention is in the field of processes for lumber treatment,including defect removal, drying and joining.

BACKGROUND OF THE INVENTION

Wood is hydroscopic, which means that it shrinks or swells with changesin its moisture content (MC). Freshly cut green lumber generally shrinksas its moisture content falls over time. Before lumber is used forconstruction, it is therefore usually desireable to dry the wood to amoisture content that will be relatively stable during the service lifeof the lumber in a particular structure, to minimize changes in the sizeof the lumber after it is used in construction. Drying may also be adesireable step in the preparation of engineered wood composits or otherwood products, or as preparatory step prior to impregantion of a woodproduct with compounds such as preservatives or fire retardants.

Drying lumber before placing it in service may have a number ofadvantages, including: providing dimensional stability; increasingstrength and mechanical fastener holding power; reducing subsequentdrying-related damage such as splitting and checking; decreasingsusceptibility to biological stain, decay and insect attack; improvingthe capacity of wood to hold paint and other coatings; and reducing theweight of wood with a resulting decrease in shipping and handling costs.

There are a number of factors that affect the process of drying lumber,including the species of tree, lumber size, structural direction ofwood, drying method, and method of lumber preparation. Theinterrelationship of these factors may be complex. For example, themoisture content of sapwood lumber is usually considerably higher thanheartwood. However, this variation in initial moisture content may beoffset in the drying process by the fact that sapwood has a higherpermeability than heartwood. In green lumber, it is possible to detectmoisture content variations between species, from pith to bark and atdifferent height levels. For example, differences among spruce, pine,and alpine fir trees may include variability in the percentage ofsapwood content between species, variability in the moisture content ofthe sapwood between species, variability in the heartwood moisturecontent between species and variability in moisture content single logfrom the sapwood-heartwood boundary to the pith region (dependednt inpart on the tree height). Exemplary data gathered from pine and alpinefir trees at different height levels, and on various spruce and alpinefir logs of different diamenters, shows the sapwood contents as given inTables 1a and 1b, respectively.

TABLE 1a Sapwood/Heartwood Ratio (%) for Spruce-Pine-Fir Trees atVarying Height Levels Tree Height (ft) Alpine Fir Spruce Pine  0 19.530.5 24.0  8 16.5 29.5 22.0 16 18.5 26.5 22.0 24 18.0 25.5 29.0 32 20.524.0 29.0 40 22.5 25.5 31.0 48 31.0 28.0 28.0 56 35.5 34.0 64 42.0 7258.0 80 71.0 Average 20.9 28.1 35.5

TABLE 1b Sapwood Content of Various Randomly Selected Spruce and AlpineFir Logs Spruce Alpine Fir Diameter Sapwood Content Diameter SapwoodContent (in) (%) (in) (%) 8.0 20.4 12.8 15.0 7.6 41.0  8.4 23.8 7.2 30.010.3 17.0 5.4 28.0 12.2 12.4 8.6 45.0 15.2 10.0 5.7 19.0  9.6 12.0 5.434.8 14.5  23.0 10.8  19.6 9.3 21.4 8.0 22.0 Average 8.2 27.7 11.4 15.0

A consequence of the wide variability in moisture content and wooddrying properties is that drying processes that typically treat largevolumes of lumber with a uniform process may give varying results fordifferent parts of the treated lumber. For example, alpine fir dried ina conventional kiln using a typical drying schedule may produce lumberwith a variable final moisture content, shown in Table 2, indicatingthat even if the average moisture content of the lumber was within aselected maximum limit (such as 19%), a large volume of the lumber maystill have a moisture content over that limit. For example, in theexemplified data, when the average moisture content was down to 18.6%,it was estimated that about 48% of the lumber still had a moisturecontent over 19%, and about 78% of the lumber had a moisture contentover 12%. This is demonstrative of inefficiencies in conventional dryingprocesses. These inefficiencies may be particularly important in someapplications, such as value-added manufacturing of composite woodproducts, where it is desired to obtain a relatively uniform dryness ineach piece of lumber that is to be used for making the composite, sothat the parts of the composite have a similar moisture content.

TABLE 2 Moisture Content (MC) of Alpine Fir Lumber at Various Stages ofDrying in a Commercial Conventional Kiln Drying Average ApproximateQuantity of Lumber Pieces ( Time (hr) MC (%) MC > 12% MC > 19% 32.5 32.695.1 86.2 44.5 23.8 88.1 68.4 55.0 18.6 77.6 48.2 74.5 10.6 38.6  4.0

Variations in wood structure and permeability, relative proportions ofsapwood and heartwood, and differences in specific gravity, originalmoisture content and moisture distribution, and refractiveness of thewood all contribute to differences in the drying properties of differentspecies. One of the causes of low permeability, as well as largevariation in permeability within a species, is the presence ofdiscontinuities in a particular piece of lumber, such as wet pockets orknots.

There are two main structural directions in wood, namely: longitudinaland transverse. The longitudinal direction corresponds to the directionalong the stem or trunk of the tree. The long dimension of most cutlumber is along this longitudinal direction of the wood. The transversedirection is perpendicular to the longitudinal direction of the stem.There are two structurally distinct transverse directions in wood,namely: radial and tangential. The radial direction is parallel to theradius of the stem, passing from the bark through the pithperpendicularly to the annual growth rings of the tree. The tangentialdirection is perpendicular to the radial direction and tangent to theannual growth rings of the tree.

The width and thickness of most cut lumber is along a transversedirection of the wood, the transverse direction typically having acomponent that is radial and a component that is tangential. Thesestructural directions in wood are important to the drying processbecause wood is in part composed of elongated water-carrying channels(some of which carry fluids other than water, such as sap, underphysiological conditions), most of which are oriented in thelongitudinal direction of the stem. The longitudinal orientation ofthese passageways dictates that lumber is an anisotropic material inwhich the rate of fluid flow is different in the transverse andlongitudinal directions.

Moisture movement in lumber is typically much slower in the transversedirection compared to the longitudinal direction. It has for examplebeen calculated that the diffusion coefficient in the longitudinaldirection may be about six times as great as that in the transversedirection (Brown, H. P., A. J. Panshin and C. C. Forsaith. 1952.Textbook of Wood Technology, Vol. II. 1^(st) Ed.). Although moisturemovement may be proportionally much more rapid in the longitudinaldirection, the usual dimensions of cut lumber dictate that moisturemigration in the transverse direction may be more important inconventional drying processes. This can give rise to difficulties indrying thick pieces of lumber, which have relatively large transversedimensions.

There are a number of known methods for drying lumber, including: airdrying, which is a relatively slow process; kiln drying, which uses hightemperatures and air circulation to increase the drying rate; radiofrequency/vacuum drying, in which the wood is heated by radio frequencyirradiation and subjected to vacuum; superheated steam/vacuum drying, inwhich the lumber is heated with superheated steam. There are drawbacksto some conventional drying methods. For example, in radio frequencydrying of lumber with a large longitudinal dimension, internal burningof the wood may occur when portions of the wood reach a relatively lowmoisture content, while other portions of the wood remain at arelatively high moisture content.

A number of innovative methods have been suggested for improvingconventional drying processes. For example, U.S. Pat. No. 5,075,131 toHattori et al. discloses a method for treatment of wood that includesforming small holes in the surface of the wood to assist in theimpregnation of the wood with a preservative and to facilitate drying ofthe wood. Such methods of introducing very small holes or incisions inthe wood may be intended to minimize surface damage, and therebypreserve the aesthetic appearance of the wood, the dimensions of theholes do not readily permit the holes to be refilled, except perhapswith a surface coating. In some applications, the presence of many smallholes in the surface of a piece of lumber may be aestheticallyundesirable.

The appearance of finished lumber may be improved by removing defectssuch as knots and knotholes. A wide variety of methods are known fordetecting and repairing naturally occuring defects in lumber. Forexample, U.S. Pat. Nos. 4,894,971 and 5,440,859 disclose methods ofreplacing defects such as knots with a shaped plug. Automated systemshave been suggested for detecting defects such as knots, and using suchinformation to grade lumber or to effect repairs. Examples of suchsystems are disclosed in U.S. Pat. No. 4,984,172 issued to Luminari in1991, U.S. Pat. No. 5,412,220 issued to Moore in 1995 and U.S. Pat. No.5,585,732 issued to Steele et al. in 1996.

SUMMARY OF THE INVENTION

In one aspect, the invention may be adapted to provide a method oftreating a piece of lumber including the steps of a) analyzing thelumber to detect a surface defect at a site on the lumber; b) removingat least a portion of the surface defect to form an opening in thelumber at the site of the defect; c) drying the lumber using a processwherein moisture is allowed to escape from the lumber through theopening; and, d) inserting a solid plug in the opening to refill theopening in the lumber.

In some embodiments, the openings in the lumber may be formed so thatthey bisect water-carrying channels in the lumber. A wide variety ofdrying processes may be used, as are known in the art. For example,vacuum and/or heat may be applied in the step of drying the lumber, andheating may be by electromagnetic irradiation. The plug may be made outof a wide variety of materials, depending on structural and aestheticrequirements. For example, the plug may be formed from wood, in whichcase the plug may be inserted so that the direction of the grain of theplug approximately matches the direction of the grain of the lumber. Theplug may also be cut from the same piece of lumber, which may assist inmatching the appearance of the plug and the surface of the lumber. Aplurality of openings may of course be formed in the lumber, and theopenings may be preferentially located in regions of the lumber thathave a high moisture content relative to other portions of the lumber,so that the drying process tends to evenly dry the lumber. The plugs maybe planed, for example in a standard planing mill, so that the plugs arelevel with a surrounding surface of the lumber. The lumber may beinfused with a liquid, such as a preservative, through the openingsbefore the plug is inserted, either before or after the lumber is dried.

Two or more pieces of lumber provided with opening in accordance withthe methods of the invention may be joined by a connector inserted intocorresponding holes in each of the pieces of lumber, to form a compositewood product.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing flexural properties of dowel-reinforcededge-glued panels bonded with PRF, showing load vs. deformation.

FIG. 2 is a graph showing flexural properties of dowel-reinforcededge-glued panels bonded with PVA, showing load vs. deformation.

FIG. 3 is a schematic representation of an automated scanning and boringsystem.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect, the present invention provides methods of treating lumberto improve drying. In preferred embodiments, such methods involveforming openings in the lumber, for example by drilling holes in thelumber. The openings may be of variable size and shape, and arepreferentially partly or fully through the transverse direction of thelumber. The opening may be disposed along the longitudinal direction ofthe lumber, and the frequency of the holes may be varied depending onproperties of the wood. The holes preferentially expose internalend-grain regions of the lumber, to facilitate the escape of moisturefrom the wood. The openings may be spaced to optimize moisture escapeunder selected drying conditions. The openings are adapted so that theymay be refilled once the lumber has been dried. In some embodiments, theholes in the lumber may be refilled with wooden plugs that approximatethe appearance of the clear regions of the lumber. In some embodiments,such plugs may be obtained from other portions of the same piece oflumber. The plugs may be oriented on insertion so that theysubstantially match the direction or grain of the wood. After the plugsare inserted into the lumber, they may be finished by planing to matchthe surface contour of the adjoining wood. Alternatively, in anotheraspect of the invention, the plugs or dowels may be used to joinseparate pieces of lumber, to form a composite wood product. Theseparate pieces of lumber may also be joined with adhesive, in whichcase the dowelling may serve to strengthen the composite wood product.

In one aspect of the invention, the plugs that are used to fill theholes in the wood may be oriented so that the grain of the plug matchesthe grain of the wood. In a preferred embodiment, the plug will beinserted through a transverse surface of the lumber, and the plug willbe similarly oriented so that the grain of the plug is not exposed. In aknot, in contrast, the grain typically runs perpendicular to the surfaceof the wood, so that the knot may act to let moisture into the wood,which may lead to rot (particularly if the knot is not sealed with asurface coating), or the knot may bleed sap that discolours or damagesany surface finish on the lumber. The present invention may be adaptedin some embodiments to avoid these problems by using appropriatelyoriented plugs to replace knots.

In one aspect, the invention may include methods of detecting regions oflumber that should preferentially be removed to provide openings thatwill be located so as to facilitate drying of the lumber. Regions oflumber having relatively high moisture content may for example beidentified for preferential removal by measuring the dielectric responseof the lumber. Voids and knots may also be detected by sensing thedielectric response of lumber, as disclosed in U.S. Pat. No. 5,585,732(which is hereby incorporated by reference). Commercial in-line moisturecontent sensing devices may also be used to identify regions of lumberhaving relatively high moisture content, so that a larger number ofopenings, or larger openings, can be made in such regions in accordancewith some embodiments of the present invention.

EXAMPLES Example 1 Effect of Drilled Holes on Lumber Drying at aControlled Temperature

A comparison was made of the drying rate of 2×4-inch green alpine firlumber, 4 feet long, with different hole sizes drilled through thenarrow face of the lumber. The hole sizes were 0 (control), ¼, ⅜, ½, and⅝ inch. Five holes were drilled on each piece, 2 inches from each endand three in the middle section spaced 11 inches apart center-to-center.The lumber was end-coated with glue to prevent or minimize moisture lossthrough the ends. The samples were dried in an oven at 40° C. for 22.9hours and at 50° C. for 111.5 hours. The weight of the samples wasmonitored during the drying period.

The results are shown in Table 3. The weight loss was relatively rapidduring the first 88 hours of drying, and then tended to level off withfurther drying. The samples with larger holes (½ and ⅝ inch) showed amore rapid weight loss than those with smaller holes and the control.The weight loss generally increased with increasing hole size. At theend of the drying period, the sample with the ⅝-inch holes showed about37% greater weight loss than the control. These results demonstrate theenhancement effect of the manufactured holes on the drying of lumber.

TABLE 3 Weight Loss of Alpine Fir Lumber with Varying Hole Size Dried inan Air-Circulation Oven (Holes drilled through narrow face) HoleDiameter Drying Time (hr) (in.) 16.4 22.9 88.6 94.3 111.5 Control 265.4304.8 632.8 646.5 684.8 ¼ 331.8 374.3 746.3 759.1 794.6 ⅜ 293.9 348.4700.0 709.8 735.2 ½ 358.0 419.3 911.0 927.3 970.5 ⅝ 429.6 499.3 1020.51036.9 1080.9

The invention was also exemplified in an embodiment in which the holeswere drilled through the wide face of pieces of lumber about 3 feetlong. In alternative embodiments, the hole sizes were 0, ⅜, ¾, and 1inch. Five holes were drilled on each piece, two about 3 inches fromeach end and three in the middle section spaced 7 inches apartcenter-to-center. The samples were dried in an oven at 68° C. for 30.7hours and at 85° C. for 39 hours. The results are shown in Table 4. Thetrend was similar to that reported in Table 3. The weight loss generallyincreased with increasing hole size. At the end of the drying period,the sample with the 1-inch hole showed about 11% greater weight lossthan the control. These results further demonstrate an enhancementeffect of the manufactured holes on lumber drying.

TABLE 4 Weight Loss of Alpine Fir Lumber with Varying Hole Size Dried inan Air - Circulation Oven (Holes drilled through wide face) Drying Time(hr) Hole Diameter Air Drying Oven Drying (in.) 16.5  23.6  88.3 4.520.8 26.8 30.8 47.8 69.8 Control 74.17 102.68  247.55 57.03 178.20216.93 247.85 372.43 469.70 ⅜ 61.10 87.47 271.63 78.72 235.48 278.93317.93 454.85 536.33 ¾ 69.13 99.03 286.75 93.48 270.43 315.55 356.50487.60 551.90 1 52.43 74.03 260.03 88.88 262.28 299.75 340.25 468.43525.98

Example 2 Effect of Drilled Holes on Lumber Drying Using MicrowaveHeating

A comparison was made of the drying rate of drilled and undrilled lumberusing microwave heating. The samples comprised 2×3×11.5 inch greenalpine fir lumber. In the first test, samples with 0, two, three, andfour holes, ¾ inch in diameter, drilled through the wide face wereprepared. For the two-hole sample the holes were spaced 3⅞ inches apart,for the three-hole 2⅞ inches apart, and for the four-hole 2{fraction(5/16)} inches apart, center-to-center at the middle portion. Thesamples were dried in a Sharp Carousel with ESP Sensor microwave oven.The samples were laid on the narrow face in two layers of two samplesper layer. The control and four-hole samples were located at the bottom,and the two-hole and three-hole samples at the top layer. The sampleswere spaced about 2 inches apart. The drying was continued until thecontrol sample showed signs of burning, ie. emission of smoke. Theweight of the samples was monitored every 2-3 minutes throughout thedrying period. At the end of the drying period, some samples were sawnin the middle along the grain to examine the characteristic of theinterior portion.

The results are shown in Table 5. The drying rate was relatively rapidduring the first 40 minutes of drying, and then gradually decreased withfurther drying. Of the samples located on the bottom layer, the controland four-hole samples, the latter showed a greater drying rate than theformer. Likewise, of the samples on the top layer, the three-hole sampleshowed a greater drying rate than the two-hole sample. At about 40minutes into the drying period, the four-hole sample showed about 9%greater drying rate than the control. Similarly, the three-hole sampleshowed about 19% greater drying rate than the two-hole sample. At about57 minutes of drying, smoke was observed being emitted by the controlsample. The interior portion of the control showed distinct charringwhich was not readily visible in the drilled samples. These resultsdemonstrate that in some embodiments the manufactured holes enhancedrying and at the same time may minimize or prevent thermal degradationof the lumber.

TABLE 5 Drying Rate of Alpine Fir Lumber with Varying Number of HolesDried in a Microwave Oven (Two Layers) Number of Holes Drying Time(minute) & Position 2 4 6 9 12 15 18 21 24 27 30 Control (Bottom) 0.580.57 0.66 0.79 0.93 1.12 1.27 1.42 1.54 1.62 1.73 4 (Bottom) 0.62 0.660.87 1.05 1.25 1.38 1.54 1.64 1.74 1.83 1.90 3 (Top) 0.49 0.54 0.67 0.780.95 1.10 1.23 1.36 1.46 1.51 1.58 2 (Top) 0.49 0.46 0.57 0.64 0.77 0.911.07 1.16 1.22 1.27 1.31 33 36 39 42 45 48 51 54 57 60 Control (Bottom)1.79 1.82 1.85 1.84 1.83 1.82 1.79 1.76 1.71 1.68 4 (Bottom) 1.94 2.012.02 2.04 2.02 1.98 1.93 1.88 1.83 1.78 3 (Top) 1.63 1.67 1.69 1.70 1.701.69 1.66 1.63 1.60 1.56 2 (Top) 1.33 1.35 1.36 1.35 1.34 1.32 1.31 1.291.26 1.23

In alternative test, samples with 0, three, and four holes were preparedas in the first test of this example. The samples were laid in themicrowave oven on the wide face of the lumber in one layer with no spacebetween samples. The three-hole sample was located in the middle, andthe control and the four-hole samples were located on each side of themiddle sample. As in the first test, the weight was monitored every 3minutes and the drying was continued until the control sample began toemit smoke.

The results for the alternative test are shown in Table 6. As in thefirst test, the drying rate was relatively rapid at the early stage ofdrying, ie. during the first 25 minutes, and then gradually decreasedwith further drying. The drilled samples showed a greater drying ratethan the control up to a few minutes past the maximum drying rateobserved for the former, ie. during the first 29 minutes. After thisdrying period, the control then showed a greater apparent drying rate(weight loss) than the four-hole sample. This was probably due to theonset of thermal degradation in the interior portion of the control, aprocess that was later manifested, at about 39 minutes into the dryingperiod, by the emission of smoke from the control sample. At the end ofthe drying period, the control showed severe interior charring followedin decreasing order by the three-hole sample and the four-hole sample.The latter sample showed only slight charring. The three-hole sampleexhibited a greater apparent drying rate than the four-hole sample, aneffect which was probably due to the position of the sample in the oven,so that the three-hole sample may have absorbed more energy because itwas located in the middle, between the other two samples, without anyspace between them. At about 25 minutes of drying, the four-hole sampleshowed about 8%, and the three-hole sample about 16%, greater dryingthan the control. These embodiments further demonstrate the effectmanufactured holes may have on enhancing the drying rate of lumber, anda surprising controlling effect on the thermal degradation of the wood.

TABLE 6 Drying Rate of Alpine Fir Lumber with Varying Number of HolesDried in a Microwave Oven (One Layer) Number of Holes & Drying Time(minute) Position 3 6 9 12 15 18 21 24 Control (Side) 0.48 0.69 1.001.36 1.64 1.86 2.03 2.09 3 (Middle) 0.44 0.78 1.31 1.86 2.25 2.42 2.472.50 4 (Side) 0.59 1.03 1.48 1.86 2.10 2.23 2.25 2.28 27 30 33 36 39 4245 Control (Side) 2.14 2.20 2.19 2.12 2.05 1.97 1.93 3 (Middle) 2.472.42 2.34 2.25 2.15 2.04 1.96 4 (Side) 2.26 2.17 2.09 2.02 1.92 1.821.72

Example 3 Effect of Thickness on Lumber Drying

In these embodiments, a comparison was made of the drying rate of greenalpine fir lumber of different thicknesses using acontrolled-temperature oven. Alpine fir lumber samples approximately 2in.×6 in.×4 feet long were use in these embodiments. The samplesincluded lumber that was full-thickness (unsplit), ½-thickness split and⅓-thickness split. The samples were dried in an oven at 50° C. for 43hours and at 85° C. for 24 hours. The weight and moisture content of thesamples were monitored during the drying period. Moisture content wasmeasured with a moisture meter. The results are shown in Tables 7 and 8for the weight loss and moisture content, respectively. The percentageweight loss was relatively rapid during the first 37 hours of drying andalso when the temperature was changed from 50° to 85° C., and thentended to level off with further drying. The ⅓-thickness split showedthe most rapid weight loss followed, in decreasing order, by the½-thickness split and the full-thickness samples. The ⅓-thickness splitsamples attained a moisture content of about 13% after only 16 hours ofdrying at 50° C. The same moisture content was attained by the½-thickness split after 37 hours at the same temperature, while thefull-thickness samples took about 65 hours (43 hours at 50° C. and 25hours at 85° C.) to reach that same moisture content. Thus, the½-thickness took more than twice as long, and the full-thickness morethan four times as long, to dry to about 13% moisture content comparedto the ⅓-split thickness samples. These data show the significant effectthat the transverse thickness of the lumber may have on the rate ofdrying in some embodiments of the invention. In some applications of themethods of the invention.

TABLE 7 Percent Weight Loss of Alpine Fir Lumber of DifferentThicknesses Dried In an Air-Circulation Oven Lumber Thickness DryingTime (hr) (in.) 15.5  20.0  37.3  42.7  60.3  67.4  1.70  3.91  4.72 7.57  9.99 14.79 16.36 0.85 10.88 12.27 15.92 20.78 23.05 0.57 13.1714.02 21.55 25.63 26.75

TABLE 8 Weight Loss of Alpine Fir Lumber with Varying Number of HolesDried in a Microwave Oven (One Layer) Number of Holes & Drying Time(minute) Position 3 6 9 12 15 18 21 24 Control (Side)  0.41  1.25  2.72 4.93  7.43 10.10 12.84 15.12 3 (Middle)  0.40  1.42  3.59  6.77 10.2313.24 15.77 18.19 4 (Side)  0.56  1.94  4.20  7.03  9.97 12.68 14.8917.25 27 30 33 36 39 42 45 Control (Side) 17.42 19.93 21.81 23.06 24.1224.95 26.16 3 (Middle) 20.25 22.05 23.47 24.63 25.50 26.07 26.74 4(Side) 19.23 20.60 21.81 22.92 23.70 24.13 24.44

Example 4 Effect of Drilled Holes on Water Absorption of Wood

In this example, a comparison was made of the water absorption of alpinefir lumber with varying hole sizes and varying number of holes. In thefirst test, the hole size was varied with the holes drilled through thewide face of the lumber. The samples used were dried lumber pieces ofapproximately 2 in.×4 in.×3 feet. The hole sizes were 0, ⅜, ¾, and 1inch in diameter. Five holes were drilled in each piece, two about 3inches from each end and three in the middle section spaced 7 inchesapart center-to-center. The samples were submerged lying flathorizontally in water at room temperature. After a 2-hour submersion,the samples were removed from the water and the excess surface water wasremoved, after which the samples were immediately weighed. This weighingprocedure was repeated for an additional submersion of 4 and 22 hours.

The results are shown in Table 9. The water absorption increased withincreasing hole size and soaking time. The rate of absorption was fasterduring the first two hours and relatively slower with further soaking upto 24 hours. After 24 hours of soaking, the ⅜-inch-hole, ¾-inch-hole,and 1-inch-hole samples showed respectively 1.5%, 12%, and 21% greaterabsorption than the control. These results demonstrate the effectmanufactured holes may have in enhancing liquid absorption by lumber. Insome embodiments of the invention, liquids such as preservatives may beinfused into the lumber through the manufactured holes before or afterthe lumber is dried.

TABLE 9 Percent Water Absorption of Drilled Alpine Fir Lumber withVarying Hole Size Hole Diameter Soak Time (hr) (in.) 2 6 24 Control 3.735.56  9.48 ⅜ 3.86 5.75  9.62 ¾ 4.44 6.65 10.77 1 5.17 7.38 12.05

In alternative test embodiments, the number of holes was varied, withsamples having 0, 3, 4 and 7 holes, while the hole size remained fixedat 1 inch. The lumber used in these tests was dried and approximately 2in.×4 in.×8 feet in nominal size. For the three-hole sample the holeswere spaced about 2 feet apart and 2 feet from each end, for thefour-hole sample the holes were spaced 1.5 feet apart and 1.75 feet fromeach end, and for the seven-hole sample the holes were placed about 1foot apart and about 1 foot from each end, center-to-center.

The results of these tests summarized in Table 10. The water absorptionby these samples increased with increasing number of holes and soakingtime. As in the first test in this example, the rate of absorption wasfaster during the first two hours and decreased with further soaking.After 24 hours of soaking, the three-, four-, and seven-hole samplesshowed respectively 15%, 16%, and 25% greater liquid absorption than thecontrol. These results further demonstrate the enhancement effect ofmanufactured holes on liquid absorption in some embodiments of theinvention.

TABLE 10 Percent Water Absorption of Drilled Alpine Fir Lumber withVarying Number of Holes Soak Time (hr) Number of Holes 2 6 24 Control3.89 5.33  8.55 3 4.52 6.33  9.97 4 4.78 6.30 10.11 7 5.31 7.16 11.43

Example 5 Effect of Drilled Holes on Lumber Drying Using SuperheatedSteam/Vacuum Method

In this example, a comparison was made of the drying of drilled andundrilled lumber using a laboratory superheated steam/vacuum (SS/V)kiln. The samples were green spruce lumber approximately 4¼ in.×4¼ in.×8feet. In the first test, samples with 0, two, three, four, and sevenholes, 1 inch in diameter, were prepared. The holes were drilled throughtwo faces of the lumber. For the two-hole sample, the holes were spaced3 feet apart and 2.5 feet from each end, for the three-hole sample theholes were placed 2 feet apart and 2 feet from each end, for thefour-hole sample the holes were placed 1.5 feet apart and 1.75 feet fromeach end, and for the seven-hole sample the holes were placed 1 footapart and 1 foot from each end, center-to-center. The samples werecombined in two packages, each 6 samples wide×3 samples high. Fourspacers, ¾-inch thick×1½-inch wide, were placed between layers of thepackages, one at each end and two equally spaced at the middle portion.

The results are summarized in Tables 11 and 12. The results showed that92% of the drilled samples and only 33% of the control samples wereacceptable based on a selected maximum average moisture content of 18%,where the average is taken from the outer, intermediate and core layersand the moisture content is determined by the ovendry method (Table 11).Based on the average moisture content of only the two outer layers, ie.the first 0.8 in. strips from the surface, 100% of the drilled samplesand only 83% of the control samples were acceptable. The number ofacceptable pieces decreased as the moisture content basis used waschanged from that of the surface to that of the core layer. For example,when the core layer moisture content was used as the basis, 75% of thedrilled samples and only 25% of the control samples were acceptable. Theaverage moisture contents of the drilled samples for the three layerswere all below 18%, with an overall average (average of all the drilledsamples) of about 13.7%, while that of the control samples was 23.3%(Table 12). The average moisture content distributions in the transverse(thickness) direction for the different treatments are shown in Table13. The drilled samples exhibited a more uniform moisture contentdistribution within each sample, compared to the control. This providesan indication that in some embodiments of the invention drilled lumberwould be more stable than undrilled lumber in its warping behaviour.These results demonstrate the effectiveness of manufactured holes mayhave in some embodiments in enhancing the drying of lumber andpotentially improving the dimensional stability of thick lumber.

TABLE 11 Percentage of Acceptable * Pieces of the Superheated SteamVacuum Dried 4 × 4 Spruce Lumber with Full Manufactured Holes MoistureContent Basis Control Drilled (2-7 Full Holes) Outer Layer 83 100 (First 0.8″ Strips from Surface) Intermediate Layer 28 83 (Second 0.8″Strips from Surface) Core 25 75 (Middle 0.8″ Strip) Overall Average 3392 * Based on a maximum moisture content of 18%.

TABLE 12 Moisture Content (MC) of the Superheated Steam Vacuum Dried 4 ×4 Spruce Lumber with Full Manufactured Holes No. of Full Holes AverageMC (%) MC (%) Range 0 23.3 12.1-41.4 2 13.7 12.9-14.7 3 17.3 12.5-26.3 410.5  9.3-12.3 7 13.1 11.1-16.3

TABLE 13 Moisture Content Distribution in the Thickness Direction of theSuperheated Steam Vacuum Dried 4 × 4 Spruce Lumber with FullManufactured Holes Moisture Content Layer (%) 7 Holes Control Outer¹13.3 14.5 Intermediate² 14.5 33.6 Core³ 16.1 42.0 4 Holes Control Outer10.3 13.9 Intermediate 11.0 16.8 Core 10.2 21.4 3 Holes Control Outer12.3 15.9 Intermediate 17.9 31.6 Core 26.2 39.5 2 Holes Control Outer12.4 16.3 Intermediate 14.5 25.4 Core 16.1 28.4 ¹First 0.8 inch stripfrom surface ²Second 0.8 inch strip from surface ³Middle 0.8 inch strip

A second test was conducted as part of this example, in which sampleswith half-through holes were included. The results of these tests areshown in Tables 14 and 15. The results showed that 100% of the drilledsamples with full holes, 93% of the samples with half holes and only 65%of the control samples were acceptable based on a selected maximumaverage moisture content of 18%, ie. the average of the three layers(Table 14). Based on the average moisture content of the outer layers,100% of the drilled samples with half or full holes were acceptablecompared to only 94% for the control. As found in the first test of thisexample, the number of acceptable pieces decreased as the moisturecontent basis was changed from that of the surface to that of the corelayer. When based on the core layer moisture content, 100% of thedrilled samples with full holes and 71% of those with half holes wereacceptable compared to only 47% for the control. The same trend wasobserved when the comparison was based on the intermediate layermoisture content. The overall average moisture content of the controlsamples was 17.8% with a range of 12.5 to 15.9% (Table 15). In contrast,the overall average moisture content of the drilled samples was lower,being 13.0% and 14.6% for those with full and half holes, respectively.The overall moisture content range for the samples with half holes was12.0 to 23.8%, and for the samples with full holes was 11.5 to 15.2%.

The moisture content distributions in the thickness (transverse)direction for the different treatments is summarized in Table 16. Thedrilled samples exhibited a more uniform moisture content distributioncompared to the control, and so did those with full holes compared tothose with half holes. Thus, in some embodiments, the full holes mayprovide more efficient drying than the half holes. These results furtherdemonstrate the effectiveness manufactured holes may have in enhancingthe drying of thick lumber in some embodiments.

TABLE 14 Percentage of Acceptable * Pieces of the Superheated SteamVacuum Dried 4 × 4 Spruce Lumber with Full and Half Manufactured HolesMoisture Content Drilled Basis Control (2-7 Full and Half Holes) HalfHoles Full Holes Outer Layer 94 100  100 (First 0.8″ Strips fromSurface) Intermediate Layer 65 93 100 (Second 0.8″ Strips from Surface)Core Layer 47 71 100 (Middle 0.8″ Strip) Overall Average 65 93 100 *Based on a maximum moisture content of 18%.

TABLE 15 Moisture Content (MC) of the Superheated Steam Vacuum Dried 4 ×4 Spruce Lumber with Full and Half Manufactured Holes No. of Hole HoleType Average MC (%) MC (%) Range 0 N/A 17.8 12.5-33.9 2 Full 15.2 — 3Full 13.2 — 4 Full 11.5 — 7 Half 12.0 — 2 Half 14.0 12.7-15.2 3 Half14.5 12.0-16.6 4 Half 15.6 12.4-23.8 7 Half 14.4 12.6-16.1

Example 6 Effect of Drilled Holes on Lumber Drying Using RadioFrequency/Vacuum Method (commercial scale)

Test embodiments similar to those disclosed in Example 5 were prepared,in which the drying facility used was a commercial radiofrequency/vacuum kiln. The samples used were 4¼ in.×4¼ in.×8 feet greenspruce-pine lumber. Full and half hole samples were prepared with 0,three, four, and seven holes. The samples were piled together in thekiln without spacers.

The results are presented in Table 17. Based on a selected maximumoverall average moisture content of 15%, 100% of the drilled sampleswith full holes and 75% of those with half holes were acceptable, whileonly 56% of the control samples were acceptable. At the same moisturecontent limit, similar values were obtained when the comparison wasbased on the average moisture content of the outer layers. The number ofacceptable pieces was lower when the comparison was based on themoisture content of the intermediate or core layers. For both of theselayers at the same moisture content limit, 86% of the drilled sampleswith full holes and 50% of those with half holes were acceptable,compared to only 33% acceptable samples for the control. When themoisture content basis was increased to 18%, 100% of the drilled sampleswith half or full holes were acceptable compared to only 89% for thecontrol when the comparison was made on the intermediate layer, corelayer or overall average moisture content. At the same moisture contentlimit, the control samples also yielded 100% acceptable pieces whenbased on the outer layer. As in example 5, the full holes provided moreefficient drying than the half holes. These results further demonstratethe effectiveness of manufactured holes in some embodiments in enhancingthe drying of thick lumber.

TABLE 16 Moisture Content Distribution in the Thickness Direction of theSuperheated Steam Vacuum Dried 4 × 4 Spruce Lumber with Full and HalfManufactured Holes Moisture Content Layer (%) 7 Half Holes ControlOuter¹ 12.3 13.4 Intermediate² 15.4 20.6 Core³ 16.4 25.6 4 Half HolesControl Outer 12.1 13.1 Intermediate 16.9 20.2 Core 19.8 23.5 3 HalfHoles Control Outer 12.8 13.9 Intermediate 15.4 21.3 Core 16.2 26.9 2Half Holes Control Outer 12.2 13.9 Intermediate 14.8 20.8 Core 15.8 24.67 Full Holes Control Outer 10.5 12.6 Intermediate 12.6 17.2 Core 13.519.6 4 Full Holes Control Outer 10.4 11.7 Intermediate 12.1 14.4 Core12.6 18.6 3 Full Holes Control Outer 12.3 14.0 Intermediate 13.7 19.2Core 14.2 23.8 2 Full Holes Control Outer 13.1 13.9 Intermediate 16.020.8 Core 17.6 24.6 ¹First 0.8 inch strip from surface ²Second 0.8 inchstrip from surface ³Middle 0.8 inch strip

TABLE 17 Percentage of Acceptable Pieces of the RF/V Dried 4 × 4Spruce-Pine Lumber with Full and Half Manufactured Holes MoistureContent Control (3-7 Drilled Full and Half Holes) Basis 15% MC 18% MC15% MC 18% MC Half Full Half Full Outer Layer 56 100  75 100  100 100(First 0.8″ Strips from Surface) Intermediate Layer 33 89 50 86 100 100(Second 0.8″ Strips from Surface) Core Layer 33 89 50 86 100 100 (Middle0.8″ Strip)

Example 7 Strength Properties of Various Types of Dowels Used in anEngineered Wood Composite Product

Tests were carried out to determine the flexural properties, such asmodulus of rupture (MOR) and modulus of elasticity (MOE), of varioustypes of dowels used to join pieces of lumber to form a composite woodproduct of the invention. The composite wood product was prepared usingdowelling to join lumber pieces, where the lumber pieces were providedwith corresponding holes for receiving the dowelling. The dowels werealuminum (⅜ inch diameter), wood (⅜, {fraction (5/16)}, ¼ inchdiameter), and plastic (⅜ inch diameter). Testing was carried out in anInstron machine. The specimens were centrally loaded on span lengths of152.4 mm, 127.0 mm, and 101.6 mm for the ⅜-, {fraction (5/16)}-, and¼-inch dowels, respectively. The load was applied continuously at a rateof motion of the movable crosshead of 4.1, 3.4, and 2.7 mm/min for the⅜-, {fraction (5/16)}-, and ¼-inch dowels, respectively.

The results are shown in Table 18. The aluminum dowel showed the highestMOR and MOE values of 80,274 psi and 8,672,425 psi, respectively,followed in decreasing order by the wood dowel, 25,430 to 30,179 psi and2,380,175 to 2,694,045 psi, and the plastic dowel, 16,656 psi and510,465 psi. Thus, the aluminum dowel was about 65% and 79% strongerthan the wood and plastic dowels, and 71% and 94% stiffer than the woodand plastic dowels, respectively.

TABLE 18 Strength Properties of Various Types of Dowels Dowel DiameterModulus of Modulus of Type (inch) Rupture (psi) Elasticity (psi)Aluminum ⅜ 80,274 8,672,425 Wood ⅜ 28,304 2,565,160 {fraction ( 5/16)}25,430 2,380,175 ¼ 30,179 2,694,045 Plastic ⅜ 16,656   510,465

Example 8 Effect of Manufactured Holes on Strength Properties of Lumber

In the first set of tests in this example, the effect of hole diameterand hole type (glued dowel and unglued dowel) on the strength properties(MOR and MOE) of the lumber was examined. The hole diameters tested were½ and 1 inch, drilled in the center and through the full thickness ofthe lumber. The material used was 2×4-inch nominal dried alpine firlumber, and the dowel used was wood. The glued dowel was bonded withcatalyzed polyvinyl acetate (PVA) adhesive. The samples were tested inflat bending in an Instron machine. The samples were centrally loaded onthe surface nearest the pith on a span of 21 inches in such a way thatthe manufactured hole was located in the center. The load was appliedcontinuously at a rate of motion of the movable crosshead of 0.10 in.(2.5 mm)/min.

The results are shown in Table 19. For the samples with the ½-inch holediameter, there were no statistically significant differences in MORvalues among the unglued dowel, glued dowel, and control (no hole),although the latter showed the highest average MOR followed, indecreasing order, by the glued dowel and unglued dowel. However, thecontrol gave significantly higher MOE than the unglued dowel, but nosignificant difference in MOE was observed between the glued dowel andcontrol. The control yielded about 8.6% greater MOE than the unglueddowel. For the samples with the 1-inch hole diameter, there were nosignificant differences in strength properties between the unglued andglued dowels, although the latter showed higher average strength valuescompared to the former. However, the control showed significantly higherstrength properties than the unglued and glued dowels. The control gaveabout 25.2% and 17.1% greater MOR and MOE, respectively, than theunglued dowel, and 17.4% and 12.5% greater MOR and MOE, respectively,than the glued dowel. These results showed that in some embodimentsgluing the dowel may improve the strength properties of wood productsmanufactured in accordance with the invention, particularly the MOE ofembodiments with smaller holes.

TABLE 19 Flexural Properties of Alpine Fir Lumber with ManufacturedHoles Hole Drilled Through Full Thickness (Glued Dowel Bonded with PVA)Tested in Flat Bending Hole Diameter MOR MOE Hole Type (inch) (psi)(psi) Unglued Dowel ½ 5,137 894,800 Glued Dowel ½ 5,266 918,855 UngluedDowel 1 4,262 812,192 Glued Dowel 1 4,703 857,143 Control N.A. 5,695979,438

In alternative tests, the effect on strength of hole depth and holediameter was examined. The hole depths tested were 0 (control), half,and full thickness, and the hole diameters tested were ½, ¾, and 1 inchdrilled on the face (wider transverse dimension) of the lumber. Threesamples (control, half, and full thickness) for each hole-diameter classwere taken from the same board. The dowels were bonded withphenol-resorcinol formaldehyde (PRF) adhesive. The procedure for testingof the samples was the same as that described above in previousexamples.

The results are shown in Table 20. For the samples with the ½-inch holediameter, there were no significant differences in the strengthproperties of the samples with varying depths of hole, although thecontrol showed the highest average strength values followed, indecreasing order, by the half hole and full hole. The results for the¾-hole diameter were similar to those of the ½-hole diameter, ie. therewere no significant differences in the strength properties of thesamples with varying hole depths, although the latter also gave thehighest average strength values compared to the drilled samples. For thesamples with the 1-inch hole diameter, the analysis indicated that forthese embodiments there were significant differences in the strengthproperties of the samples with varying hole depths. For MOR, thesignificant differences were observed between the full hole and controland between the half hole and control, but there was no significantdifference between the full hole and half hole although the latteryielded a higher average MOR value than the full hole. The controlshowed about 30.9% and 21.4% greater MOR than the full hole and halfhole, respectively. For MOE, the only significant difference observedwas between the full hole and control. No significant differencesexisted between the full hole and half hole and between the half holeand control, although the half hole gave a higher average MOE than thefull hole and that the control yielded a higher average MOE than thehalf hole. The control showed about 14.8% greater MOE than the fullhole. These data indicate that in some embodiments manufactured holeswhich are plugged with glued wood dowel may not significantly affect thestrength properties (MOR and MOE) of the lumber in bending. In addition,manufactured holes up to 1 inch in diameter, drilled only up to half thethickness of the lumber and plugged with a glued wood dowel, may beadapted so as not to significantly affect the stiffness (MOE) of thelumber in bending, although the strength (MOR) may be reduced.

TABLE 20 Flexural Properties of Alpine Fir Lumber with ManufacturedHoles Hole Drilled on Face (Dowel Glued with PRF) Tested in Flat BendingDepth of Hole Diameter MOR MOE Hole (inch) (psi) (psi) Full ½ 4602875,550 Half ½ 5086 891,678 Control N.A. 5391 908,520 Full ¾ 4394862,050 Half ¾ 4694 872,420 Control N.A. 5147 891,400 Full 1 4169830,850 Half 1 4740 898,080 Control N.A. 6034 975,470

Example 9 Dimensional Stability of a New Engineered Wood CompositeProduct

Tests were conducted to compare the warping properties of the engineeredwood composite product of the invention made by edge gluing lumberpieces joined with various types of dowels. Panel samples, 18 incheswide (in the transverse direction, across the grain)×48 inches long (inthe longitudinal direction, along the grain), were prepared from2×4-inch green alpine fir lumber glued with PRF adhesive. The panelswere constructed from five lumber pieces in such a way that the adjacentpieces had the same grain orientation. Three types of dowels were used,namely aluminum, wood, and plastic, all with ⅜-inch diameter. Fourdowels were inserted across the width, two 3 inches from each end andtwo in the middle section spaced 14 inches apart center-to-center. Thedowels were inserted through holes drilled on the narrow face of thelumber just before pressing the pieces together to form the compositepanel. Similar panels were prepared without dowels to serve as controls.

The warping (bow, cup, and twist) of the panels was measured about threeto four weeks after they were made, at which time the average moisturecontent was then about 13% as measured by a moisture meter. The resultsare shown in Table 21. The warping values of the dowel-reinforced panelswere lower than those of the controls. These results demonstrate thepositive effect of the dowels in improving the dimensional stability ofthe composite panels of the invention.

TABLE 21 Dimensional Stability of a New Engineered Wood CompositeProduct Initial MC (%) Bow Cup Twist Dowel MC (%) at Test (mm) (mm) (mm)Aluminum >20 13.1 0.8 4.7 0 Wood 25.1 11.7 0 3.3 0 Plastic 21.4 13.2 1.35.0 1.3 Control 29.2 12.6 2.2 5.4 10.5

Example 10 Strength Properties of the Engineered Wood Composite Product

Panel samples similar to those disclosed in Example 9, but with theadjacent pieces arranged in alternating grain orientation, were made tocompare the effects of dowel type on the strength properties of thepanels. The adhesives used were PRF and catalyzed PVA.

Strips, 2 inches wide, were cut across the width of the panels. Thestrips included samples with and without dowels for comparison. Thesamples were tested in bending to compare the MOR, MOE, and energyabsorption perpendicular to the grain, in which the test span isperpendicular to the grain (longitudinal) direction of the wood. Testingwas carried out in an Instron machine. The specimen was centrally loadedon a span length of 15.5 inches (393.7 mm). The load was appliedcontinuously at a rate of motion of the movable crosshead of 2.5 mm(0.10 in.)/min. The test was continued to about a 2-inch (50-mm)deflection, or until the specimen failed to support a load of about 35lb.

The results are shown in Table 22. The reinforced samples exhibitedgreater MOR, MOE, and energy absorption than the control. For PRF, thereinforced samples yielded 2.6 to 4.4 times greater MOR, 1.4 to 1.6times greater MOE, and 9 to 31 times greater energy absorption, than thecontrol. Similarly for PVA, the reinforced samples gave 1.4 to 2.8 timesgreater MOR, 1.1 to 1.7 times greater MOE, and 2.6 to 19 times greaterenergy absorption, than the control. The aluminum showed the highestMOR, MOE, and energy absorption compared to the wood and plastic dowels.The most significant difference was observed in the energy absorptionfor which the aluminum yielded more than 3 times greater than that ofthe wood dowel in the case of the PRF, and more than 7 times greater inthe case of the PVA glued samples. It exhibited as much as 31 times and19 times greater energy absorption than the control for the PRF and PVAglued samples, respectively. Comparisons of the load-deformation curvesfor the samples reinforced with the different types of dowels are showngraphically in FIGS. 1 and 2 for the PRF and PVA glued samples,respectively. The aluminum consistently showed the highest load capacitycompared to the other two dowels, and the control showed the lowestvalue. These results are consistent with those of Example 7 in which thealuminum dowel exhibited the greatest bending strength compared to thewood and plastic dowers.

TABLE 22 Strength Properties and Energy Absorption of a New EngineeredComposite Wood Product Perpendicular to the Grain Energy Absorp- MOE MOREnergy tion Ratio Ratio Absorp- Ratio MOE (Dowel/ MOR (Dowel/ tion(Dowel/ Dowel (psi) Control) (psi) Control) (in - lb) Control) PRFAdhesive Aluminum 32,216 1.60 729 4.39 220.4 31.0 Wood 28,722 1.43 4332.61 64.3 9.1 Plastic Control 20,088 166 7.1 (No dowel) PVA AdhesiveAluminum 39,163 1.65 818 2.75 234.2 18.9 Wood 37,671 1.59 405 1.36 32.82.6 Plastic 25,568 1.08 423 1.42 123.3 9.9 Control 23,753 297 12.4 (Nodowel)

Example 11 Shear Properties of the Engineered Wood Composite Product.

Block shear samples, 2 inches along×1½ inches across the grain (in thetransverse direction) with the glueline in the middle of the latterdirection, were prepared from the panels described in Example 10.Samples were tested with and without dowels for comparison. Samples weretested in shear (horizontal and rolling) to compare shear strength andenergy absorption. Testing was carried out in an Instron machine. Theload was applied continuously at a rate of motion of the movablecrosshead of 0.024 in. (0.6 mm)/min. The test was continued to about a0.75-inch (19-mm) displacement, or until the specimen failed to supporta load of about 35 lb.

The results are shown in Table 23. The horizontal shear was greater thanthe rolling shear strength. For PRF, the reinforced samples showedhorizontal-to-rolling shear ratios of about 1.9 to 2.6, and that of thecontrol was higher, ie. 3.6. Similarly for PVA, the reinforced samplesgave ratios of about 2.0 to 3.7, and the control 4.7. The lower ratiosfor the reinforced samples indicate that they were more uniform in shearproperties in both directions than the control. The reinforced samplesgenerally showed slightly lower horizontal shear strength, but greaterrolling shear strength and energy absorption than the control. In someembodiments, rolling shear strength and energy absorption may beconsidered to be more important properties than horizontal shearstrength. For PRF, the reinforced samples yielded about 1.4 to 1.8, andfor PVA 1.3 to 1.8, greater rolling shear strength than the control. Thealuminum showed the greatest rolling shear strength compared to the woodand plastic dowels. The most significant difference observed between thereinforced samples and the control was in terms of the energy absorptiondeveloped. For PRF, the reinforced samples yielded about 3 to 6 times,and for PVA 2 to 9 times, greater energy capacity than the control.These results provide further evidence of the ability of the reinforcedcomposite panels to sustain applied stress, in this case shear stress,for a long period of time.

TABLE 23 Shear Strength Properties and Energy Absorption of a NewEngineered Wood Composite Product Dowel Block Shear Shear Strength (psi)Energy Absorption (in - lb) Type Type PRF H/R PRF/C PVA H/R PVA/C PRFPRF/C PVA PVA/C Aluminum Horizontal (H) 1247 1.94 0.96 1192 2.04 0.78543.43 4.77 619.45 4.39 Rolling (R)  642 1.79  585 1.79 463.10 4.66657.62 8.69 Plastic Horizontal 1236 2.56 0.95 1448 2.80 0.94 449.46 3.94637.60 4.52 Rolling  483 1.35  518 1.59 304.99 3.07 390.18 5.15 WoodHorizontal 1191 2.16 0.92 1588 3.72 1.04 586.55 5.14 276.88 1.96 Rolling 552 1.54  427 1.31 613.89 6.18 236.76 3.15 Control (C) Horizontal 12973.61 1533 4.70 114.02 141.04 (No Dowel) Rolling  359  326  99.31  75.70

Example 12 Strength Properties of the Engineered Wood Composite ProductUsing Large Test Samples

Board samples, 9.25 inches wide (across the grain)×12 feet long (alongthe grain), were prepared by edge gluing nominal 2×4-inch dried alpinefir lumber. The boards were constructed from three lumber pieces in sucha way that the adjacent pieces had alternating grain orientation. Thebonding agent used was PRF adhesive. Aluminum dowel, ⅜-inch in diameter,was used as the reinforcement. The dowels were inserted across thewidth, two 3 inches from each end and 11 in the middle section spacedapproximately 1 foot apart. The dowels were inserted through holesdrilled on the narrow face of the lumber before pressing the board. Asimilar board was prepared without dowels to serve as control. Theboards were tested in bending to compare the MOE, MOR, and energyabsorption parallel to the grain, ie. the test span was parallel to thegrain direction of the wood. The flatwise MOE was determined on thewhole board using a span-to-depth ratio of 90:1 (span of 135 inches) inaccordance with the ASTM 4761 standard. A pre-load of 5 lb was used.Deflection measurements were taken at three increments of approximately10 lb each. After the MOE was determined, the board was cut into fourspecimens, about 4 feet long along the grain, for the determination ofMOR. The MOR specimens were tested at third-point loading also inaccordance with the ASTM 4761 standard using a span-to-depth ratio of21:1 (span of 31.5 inches). The loading configuration at each of thethird points were two concentrated loads spaced 6.75 inches apart andcentered across the width of the specimen. The load was appliedcontinuously at a rate of motion of the movable crosshead of 0.20in./min. The test was continued until the specimen failed to support 60%of the maximum load attained.

The results are shown in Table 24. The reinforced sample exhibitedgreater strength properties, ie. about 6.4% greater MOE, 16.5% greaterMOR, and 26.4% greater energy absorption, than the control. Theseresults further demonstrate the positive attribute of the reinforcedpanel in sustaining greater applied flexural load.

TABLE 24 Strength Properties and Energy Absorption Parallel to the Grainof the New Engineered Composite Wood Product Reinforced with AluminumDowel MOE MOR Energy Treatment (10⁵ psi) (psi) Absorption (in-lb)Reinforced 1.41 8085 3070 Control (No Dowel) 1.32 6755 2259

Example 13 Manufactured Clear, Dry Lumber

This example discloses a method for treating a piece of lumber to detectdefects, such as knots, with electro-optic scanning, and then replacingthe defects with plugs, which may be made of clear wood. The plugs,which may be either the full or partial thickness of the lumber, may bebonded to the lumber with an adhesive.

As is partially shown schematically in FIG. 3, the exemplified system iscomprised of an electro-optic scanning sub-system that scans, analysesthe resulting image, detects defects and then communicates co-ordinatesof the defects and related information to a machining unit sub-system. Amachining unit sub-system performs boring operations, and may alsoperform gluing and plugging operations in alternative embodiments. Theentire process may be automated using general purpose computers andsoftware in conjunction with industrial automation devices.

The scanning subsystem may be comprised of a lumber feeding system,electro-optical scanners, a computer with data acquisition hardware andthe requisite software. In such a system, lumber is fed through thefields-of-view of the scanner by a motorized conveyor system. The lumberimages collected by the scanners are digitally processed and comparedfor parameters characteristic of defects fit for replacement, such as anempirically determined colour difference threshold. Once the defect isidentified, the size, shape, and location of the defect may beidentified and this information may be stored for subsequent processingat the machining sub-system.

The software used in the scanning sub-system may be an integratedprogram responsible for controlling the acquisition of images,processing the digital data, defect detection by characterization of thedefect properties and communication of this information. Such softwaremay for example be written in the C++ programing language. The userinterface, skeleton of the program, defect detection algorithms andother components may be tailored using some functions available ascomponents of software libraries available with data acquisitionhardware. For example, the XVL or Extended Vision Library available withframe grabbers from Dipix Technologies Inc. may be used.

Data for each piece of lumber, such as the co-ordinates of the defects,may be communicated by the scanning subsystem to the boring and pluggingsubsystem via an electronic network. This data may then be processed bya general purpose computer, programmed to control the feed system andpositioning of the boring assembly. Such software may for example bewritten in the graphical programming language, Labview, available fromNational Instruments Corp. The user interface and skeleton (sequencingand timing structure) of the program may be adapted for variousembodiments of the invention.

The boring bit may be plunged either completely through the lumber or toa predetermined depth. The sequence may be repeated for each defectidentified for removal. Up to four sides of the lumber may be subjectedto processing, either individually or sequentially.

Example 14 Dimensional Stability in Manufactured Clear, Dry Lumber

Wood expands and contracts as its moisture content changes. Thisdimensional instability can over time damage wood, particularly if partsof a piece of lumber, or parts of a wooden assembly expand and contractat different rates.

This example involves the examination of the dimensional stability oflumber having knots replaced with plugs in accordance with the presentinvention, compared to lumber having knots. Five 2″×4″×8″ lodgepole pinesamples each containing three replacement plugs were prepared. Thesesamples were measured for original weights and dimensions. The initialmoisture contents were determined using the oven dry method.

The samples were then soaked for three concurrent 24-hour periods and atthe end of each period the dimension, weight and moisture contentchanges were determined. Following the final soak period, the sampleswere dried to their original moisture content and the final weights,dimensions and moisture contents were again recorded.

Ten 2″×4″×8″ samples each containing one knot were also prepared, testedand measured in exactly the same manner as the samples with the knotsremoved and the holes plugged and glued.

Table 25 summarizes the average measurements obtained from the pinesamples. It demonstrates that in this embodiment the replacement plugresponds to the water soak test in essentially the same manner as thatof clear wood. At the same time, knots react quite different whenexposed to the same conditions with inferior results to the replacementplugs.

The average difference between the thickness swelling of the plug andthe wood surface was an absolute value of 0.035 mm, while the averagedifference for the samples containing knots as 2.9 times greater than0.101 mm. This increase indicates that in these embodiments thereplacement plug is much more dimensionally stable with respect to thewood surface than are knots. This study also was conducted on sitkaspruce, alpine fir, western hemlock, and Douglas fir. Similar resultswere obtained for all 4 species.

TABLE 25 Clear Wood System Water Soak Experiment Measurement ofThickness Swelling MC Knot Wood Difference (%) (mm) (mm) (mm) Plug vs.Wood Original 11.38 0.000 0.000 0.000 24 hr 24.48 0.535 0.558 0.023 48hr 27.00 0.566 0.610 0.044 72 hr 29.43 0.695 0.650 0.045 Final 11.960.221 0.250 0.029 Average 0.035 Knot vs. Wood Original 11.68 0.000 0.0000.000 24 hr 23.51 0.643 0.530 0.113 48 hr 27.12 0.783 0.657 0.126 72 hr29.97 0.768 0.700 0.068 Final 11.16 0.100 0.196 0.096 Average 0.101

Example 15 Strength Properties of Manufactured, Clear, Dry Lumber

Tests were conducted to compare the strength properties (MOR and MOE) oflumber with knots and clear, dry lumber treated in accordance with theinvention having plugged knot holes. The material used was 2×4-inchnominal dried lodgepole pine lumber. The diameter of the knots on theknotty lumber ranged from about 24 to 30 mm (0.94 to 1.18 inches). Thediameter of the hole which was bored on the wider face through the fullthickness of the lumber was 1.5 inches (38.1 mm). The hole was pluggedwith glued wood dowel the grain direction of which was parallel to thelength of the lumber. The glued dowel was bonded with catalyzed PVAadhesive. Only one knot or plugged hole was present in the test sampleand was located at the centre of the piece. The samples were tested inflat bending in an Instron machine. The samples were centrally loaded onthe surface nearest the pith on a span of 21 inches in such a way that aknot or plugged hole was located at mid-span. The load was appliedcontinuously at a rate of motion of the movable crosshead of 0.10 in.(2.5 mm)/min.

The results are shown in Table 26. The samples with plugged holesexhibited greater strength properties, i.e. about 16.8% greater MOR and11.5% greater MOE, than the samples with knots. These results may beconservative, considering that the sizes of the knots are very muchsmaller than that of the plugged holes. A regression analysis of theknot size versus MOR indicated that if the size of the knot was the sameas that of the plugged hole, i.e. 1.5 inches, the estimated MOR of theknotty lumber was only about 5,454 psi, which was 24% lower than that ofthe plugged-hole lumber. These results show that the removal of the knotand plugging of the resulting hole may improve the strength propertiesof the lumber. Other advantages of the knot removal and plugging inalternative embodiments may include improved dimensional stability andsurface appearance, reduced checking, uniformity of density and graindirection, and improved paintability and overlaying properties of theresulting surface.

TABLE 26 Comparison of the strength properties of lumber with knot andplugged hole. Modulus of Rupture (psi) Modulus of Elasticity (psi)Lumber Type Average Std. Dev.* Average Std. Dev.* With Knot 6167 6351007614 72573 With Plugged 7200 765 1123179 62831 hole *StandardDeviation

What is claimed is:
 1. A method of treating a piece of lumbercomprising: a) analyzing the lumber to detect a surface defect at a siteon the lumber; b) removing at least a portion of the surface defect toform an opening in the lumber at the site of the defect; c) drying thelumber using a process wherein moisture is allowed to escape from thelumber through the opening; d) inserting a solid plug in the opening torefill the opening in the lumber.
 2. The method of claim 1 whereinvacuum is applied in the step of drying the lumber.
 3. The method ofclaim 2 wherein heat is applied in the step of drying the lumber.
 4. Themethod of claim 3 wherein heat is applied by electromagnetic irradiationof the lumber.
 5. The method of claim 4, wherein the plug is bonded tothe opening in the lumber with an adhesive.
 6. The method of claim 5wherein the plug is made of wood and the plug is inserted so that thedirection of the grain of the plug approximately matches the directionof the grain of the lumber.
 7. The method of claim 6 wherein a pluralityof openings are formed in the lumber and the openings are preferentiallylocated in regions of the lumber that have a high moisture contentrelative to other portions of the lumber.
 8. The method of claim 7wherein the plug is cut from the lumber.
 9. The method of claim 8further comprising the step of infusing the lumber with a liquid throughthe opening before the plug is inserted.
 10. The method of claim 9further comprising the step of planing the plugs so that the plugs arelevel with a surrounding surface of the lumber.
 11. The method of claim9 further comprising the step of providing first and second pieces oflumber treated in accordance with steps (a) through (c), wherein theopenings in the lumber are corresponding, further comprising joining thefirst and second pieces of lumber to form a composite wood product byplacing the pieces of lumber together and engaging the plug in thecorresponding openings.
 12. The method of claim 1 further comprising thestep of providing first and second pieces of lumber treated inaccordance with steps (a) through (c), wherein the openings in thelumber are corresponding, further comprising joining the first andsecond pieces of lumber to form a composite wood product by placing thepieces of lumber together and engaging the plug in the correspondingopenings.
 13. A method of drying a piece of lumber comprising: a)forming a transverse opening in the lumber bisecting water-carryingchannels in the lumber; b) drying the lumber using a process whereinmoisture is allowed to escape from the lumber through the opening; c)inserting a solid plug in the opening to refill the opening in thelumber.
 14. A method of forming a composite wood product from first andsecond pieces of lumber, comprising: a) forming corresponding transverseopenings in the first and second pieces of lumber, each openingbisecting water-carrying channels in the piece of lumber; b) drying thepieces of lumber using a process wherein moisture is allowed to escapefrom the lumber through the opening; c) joining the pieces of lumber toform the composite wood product by placing the pieces of lumber togetherand engaging a plug between each of the corresponding transverseopenings.
 15. The method of claim 14 wherein vacuum is applied in thestep of drying the lumber.
 16. The method of claim 15 wherein heat isapplied in the step of drying the lumber.
 17. The method of claim 16wherein heat is applied by electromagnetic irradiation of the lumber.18. The method of claim 17 wherein the plug is bonded to the openings inthe lumber with an adhesive.